Episodes of early Pleistocene West Antarctic ice sheet retreat recorded by iceberg alley sediments

• Published in: Paleoceanography and Paleoclimatology
• Main Authors: Bailey, I, Hemming, S, Reilly, BT, Rollinson, G, Williams, T, Weber, ME, Raymo, ME, Peck, VL, Ronge, TA, Brachfeld, S, O'Connell, S, Tauxe, L, Warnock, JP, Armbrecht, L, Cardillo, FG, Du, Z, Fauth, G, Garcia, M, Glueder, A, Guitard, M, Gutjahr, M, Hernandez-Almeida, I, Hoem, FS, Hwang, JH, Iizuka, M, Kato, Y, Kenlee, B, Martos, YM, Perez, LF, Seki, O, Tripathi, S, Zheng, X
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley-Blackwell Publishing Inc. 2022
• Subjects: Earth Sciences; Oceanography; Oceanography not elsewhere classified; Antarctic; Weddell Sea; West Antarctica; Scotia Sea; Amundsen Sea; West Antarctic Ice Sheet; Pacific; Weddell; Antarc*; Antarctica; Ice Sheet; Iceberg*
• Online Access: https://doi.org/10.1029/2022PA004433; http://ecite.utas.edu.au/155091

Ice loss in the Southern Hemisphere has been greatest over the past 30 years in West Antarctica. The high sensitivity of this region to climate change has motivated geologists to examine marine sedimentary records for evidence of past episodes of West Antarctic Ice Sheet (WAIS) instability. Sediments accumulating in the Scotia Sea are useful to examine for this purpose because they receive iceberg-rafted debris (IBRD) sourced from the Pacific- and Atlantic-facing sectors of West Antarctica. Here we report on the sedimentology and provenance of the oldest of three cm-scale coarse-grained layers recovered from this sea at International Ocean Discovery Program Site U1538. These layers are preserved in opal-rich sediments deposited ∼1.2 Ma during a relatively warm regional climate. Our microCT-based analysis of the layer's in-situ fabric confirms its ice-rafted origin. We further infer that it is the product of an intense but short-lived episode of IBRD deposition. Based on the petrography of its sand fraction and the Phanerozoic 40Ar/39Ar ages of hornblende and mica it contains, we conclude that the IBRD it contains was likely sourced from the Weddell Sea and/or Amundsen Sea embayment(s) of West Antarctica. We attribute the high concentrations of IBRD in these layers to dirty icebergs calved from the WAIS following its retreat inland from its modern grounding line. These layers also sit at the top of a ∼366-m thick Pliocene and early Pleistocene sequence that is much more dropstone-rich than its overlying sediments. We speculate this fact may reflect that WAIS mass-balance was highly dynamic during the ∼41-kyr (inter)glacial world.